Prosthetic foot technology has advanced considerably in the past 20 or so years to the point where an amputee has available a wide variety of styles. Key performance considerations include ease and stability of alignment, axial and torsional strength, as well as ease of replacement. That is, it is important that a prosthetic foot maintain both its vertical alignment, as well as resist twisting. Due to the axial compressive forces exerted on the prosthetic device along the alignment axis, the prosthetic device must also have significant axial strength.
While the performance of the prosthetic foot is very important, however, so is the cost. That is, to the extent that the cost renders the prosthetic foot unavailable for use by a given wearer, the performance characteristics of the prosthetic device are irrelevant for that wearer. Accordingly, significant effort has been made to reduce the cost of materials and manufacturing for prosthetic devices.
With most prosthetic devices now in use, the prosthetic device is fitted directly to the amputation socket and once the prosthesis is attached to the socket, it cannot be removed. Any change of prosthesis requires a complete change of the amputation socket along with the prosthesis. The fitting of the prosthesis to the amputation socket requires careful alignment and adjustment and is thus expensive.
One attempt at joining a prosthetic foot to a stump of a wearer is disclosed in U.S. Pat. No. 4,959,073 to Merlette. An upper leg portion is first bonded to a sleeve which fits tightly within a housing. The housing is aligned within the stump and secured with overwraps of composite material. This specialized attachment assembly is not yet in widespread use.
More commonly, a lower leg pylon extends between a stump of the amputee and a prosthetic foot. There are many means for connecting the pylon to the prosthetic foot, typically involving various clamps and fasteners. Such fastening means add weight and can loosen after extended use. Furthermore, the attachment mechanisms presently available require special tools and tightening standards, and introduce small parts which might be damaged or lost.
Thus, there is a need for a simple, inexpensive prosthetic foot which can be securely fastened to standard leg pylons which does not require bulky or inconvenient fastening mechanisms.